Related papers: On Graceful Exit in String Cosmology with Pre-Big …

"Brane supersymmetry breaking" occurs in String Theory when the only available combinations of D-branes and orientifolds are not mutually BPS and yet do not introduce tree-level tachyon instabilities. It is characterized by the emergence of…

The zero modes and current carrying capability of a cosmic string formed at one phase transition can be modified at subsequent phase transitions. A new, generalised index theorem is derived that is applicable to theories with multiple phase…

An accelerating Universe can be accommodated naturally within non-critical string theory, in which scattering is described by a superscattering matrix \$ that does not factorize as a product of $S$- and $S^\dagger$-matrix elements and time…

We explore the generic motion of cosmic (super)strings when the internal compact dimensions are warped, using the Klebanov-Strassler solution as a prototypical throat geometry. We find that there is no dynamical mechanism which localises…

One of the main virtues of string gas cosmology is that it resolves cosmological singularities. Since the Universe can be approximated by a locally asymptotically de Sitter spacetime by the end of the inflationary era, a singularity theorem…

In the present thesis, the author reviews the physics of cosmological first-order phase transitions that may have occured shortly after the Big Bang. Such transitions proceed via the nucleation and expansion of true vacuum bubbles and give…

String theory avoids the ultraviolet infinities that arise in trying to quantize gravity. It is also more predictive than conventional quantum field theory, one aspect of this being the way that it contributed to the emergence of the…

We have discussed a particular class of exact cosmological solutions of the 4-dimensional low energy string gravity in the string frame. In the vacuum without matter and the 2-form fields, the exact cosmological solutions always give…

We exploit the techniques of dynamical systems to study the cosmological evolution of cosmic fundamental strings and effective strings arising from branes wrapped on internal cycles. We also include the whole potential of the volume modulus…

We propose a new holographic C-function for the accelerating universe defined in the stringy frame motivated mainly by the fact that the number of degrees of freedom should be infinite for a physical system of infinite size. This is the…

We study time-dependent solutions in M and superstring theories with higher order corrections. We first present general field equations for theories of Lovelock type with stringy corrections in arbitrary dimensions. We then exhaust all…

Nonlinear electrodynamics, which acts as a source of gravity Einstein field equations, leads to emergent cosmology, an alternative solution which can avoid Big Bang singularity. In this paper, we explore the emerging universe in models of…

We derive and study a class of cosmological and wormhole solutions of low-energy effective string field theory. We consider a general four-dimensional string effective action where moduli of the compactified manifold and the electromagnetic…

In certain implementations of the brane inflationary paradigm, the exit from inflation occurs when the branes annihilate through tachyon condensation. We investigate various cosmological effects produced by this tachyonic era. We find that…

Supersymmetry breaking in string theory is expected to occur when moduli fields acquire non-trivial expectation values. In the early universe these fields start out displaced from their final destinations. I present some recent ideas about…

Cosmic strings, a hot subject in the 1980's and early 1990's, lost its appeal when it was found that it leads to inconsistencies in the power spectrum of the measured cosmic microwave background temperature anisotropies. However,…

Pre--big bang models of inflation based on string cosmology produce a stochastic gravitational wave background whose spectrum grows with decreasing wavelength, and which may be detectable using interferometers such as LIGO. We point out…

The cosmological constant problem can be understood as the failure of the decoupling principle behind effective field theory, so that some quantities in the low-energy theory are extremely sensitive to the high-energy properties. While this…

Assuming that the early universe had (i) a description using perturbative string theory and its field theory limit (ii) an epoch of slow-roll inflation within a four-dimensional effective field theory and a hierarchy of scales $M_{inf} <…

We propose a mechanism borrowed from string theory which yields a non-singular transition from a phase of Ekpyrotic contraction to the expanding phase of Standard Big Bang cosmology. The same mechanism converts the initial vacuum spectrum…